The present invention relates to fuel system valves, and particularly to a roll-over valve for closing a venting passageway in a vehicle fuel system if the vehicle is rolled over in an accident. More particularly, the present invention relates to a fuel tank pressure-regulated roll-over valve having a vapor release valve for selectively discharging a controlled volume of fuel vapor from the fuel tank to the atmosphere.
Vehicle fuel systems are known to include pressure-relief roll-over safety valves mountable on either fuel tanks or filler necks. These conventional valves are not equipped to discharge fuel vapor from the fuel system directly into the atmosphere. Hereinafter, these conventional valves will be referred to as "closed system fuel tank valves."
Closed-system fuel tank valves are known to include a pressure-relief system for discharging fuel vapors from the fuel tank to a conventional vapor treatment canister filled with activated charcoal or other substrate. It is also known to couple a separate roll-over safety system to the venting pressure-relief system. The roll-over safety system prevents hazardous discharge of fuel from the fuel tank through the venting pressure-relief system during vehicle rollover and fuel sloshing.
Typically, the closed-system fuel tank valve includes a fluid/vapor-conducting passageway interconnecting the pressure-relief and roll-over safety systems. Roll-over safety systems are known to include a valve ball housing having therein a freely movable valve ball and valve stem. When the fuel tank valve is tilted relative to a normal upright orientation during vehicle rollover and when the valve ball is ramped during vehicle acceleration and deceleration, the valve ball causes the valve stem to close the passageway thereby blocking discharge of fuel and fuel vapor from the fuel tank to the canister and atmosphere.
Operating problems have been observed with engines (particularly, engines having fuel injection systems) in vehicles having conventional "closed-system fuel tank valves". In particular, these engines do not perform very well under hot environmental conditions. These engine performance problems are caused chiefly by conventional closed-system fuel tank valves that discharge an excessive mass of fuel vapor from the fuel tank into the canister. If liquid fuel overloads the carbon surface in the canister with difficult to purge heavy hydrocarbons, then system efficiency will be reduced to a low level.
Droplets of fuel entrained in the fuel vapor are adsorbed onto the carbon substrate in the canister. Filtered air sweeps through the canister charcoal bed in response to a pressure-differential applied to the canister simultaneously desorbing the stored fuel vapors and conducting the desorbed vapors into the engine intake manifold. Engine performance is hampered by introduction of excess fuel into the engine resulting from discharge of excess fuel vapor into the canister. Mounting the canister in a high position relative to the fuel tank to lessen carryover potential has proven to be unfeasible and impractical due to packaging requirements.
An improved fuel tank valve having a purge valve means for selectively releasing fuel vapor directly to the atmosphere would advantageously minimize fuel tank pressure. At the same time, the improved valve would reduce fuel vapor mass flow to the canister, thereby reducing the mass of fuel drawn into the engine from the canister, enhancing engine performance, and avoiding shortcomings of known fuel tank valves.
According to the present invention, a roll-over valve is provided for use in a vehicle fuel system to satisfy government regulations requiring that sufficient precautions be taken to prevent fuel from leaking out of the vehicle fuel tank into a vent line leading to the canister and/or the atmosphere when the vehicle is subjected to a prescribed vehicle rollover test. The roll-over valve includes a hollow valve housing, a valve member in the valve housing, and base means for retaining the valve member in the valve housing. In addition, a ball is provided for moving the valve member within the valve housing in response to tilting movement of the valve housing relative to a normal upright position and abrupt change in vehicle motion. For example, tilting generally occurs when the vehicle is rolled over in an accident.
The hollow valve housing includes a longitudinal axis, an inlet for admitting fuel vapors from the vehicle fuel system into the valve housing, and an outlet for discharging the fuel vapors from the valve housing. The valve member is positioned within the hollow valve housing for movement generally along the longitudinal axis between an outlet-opening position and an outlet-closing position. The valve member includes a ball-receiving cup configured to define a novel first inclined ramp portion.
The base means retains the valve member within the housing and includes a second inclined ramp portion. The base means is coupled to the valve housing to present the second inclined ramp portion in opposing spaced-apart relation to the novel first inclined ramp portion of the cup to define a ball-receiving space therebetween. The ball is positioned in the ball-receiving space in substantially camming relation to each of the opposing first and second inclined ramp portions. The ball rides on both ramp portions to move the valve member to its outlet-closing position in response to tilting the valve housing about its longitudinal axis during a vehicle rollover and during abrupt change to vehicle motion.
In preferred embodiments of the present invention, the roll-over valve includes vapor distribution means for discharging a substantially constant volumetric flow rate of fuel vapor from the hollow valve housing to a vapor storage canister within the vehicle fuel system. The roll-over valve also includes vapor release means for selectively discharging a controlled volume of fuel vapor from the hollow valve housing to the atmosphere. The vapor release means advantageously minimizes fuel system pressure and reduces the mass flow rate of fuel vapor to the vapor storage canister. In other preferred embodiments, the roll-over valve can include vent means for regulating the pressure in the fuel tank.
Illustratively, the first inclined ramp portion is substantially defined by a downwardly-extending generatrix, and the second inclined ramp portion is substantially defined by an upwardly-extending generatrix. In particular, the downwardly-extending generatrix has an included angle with the longitudinal axis of the valve housing of about 70.degree., and the upwardly-extending generatrix also has an included angle with the longitudinal axis of the valve housing of about 60.degree. to 70.degree..
One feature of the present invention is the provision of opposing first and second inclined ramp portions cooperatively engaging the valve member-moving ball in substantially camming relation. This "double-ramp" feature effectively increases the travel of the valve member along the longitudinal axis of the housing during tilting of the valve housing caused by vehicle rollover or abrupt changes in vehicle without requiring a corresponding increase in the travel of the ball along the longitudinal housing axis. Advantageously, the "double-ramp" feature of the present invention increases valve member "lift" without enlarging either the interior of the hollow valve housing or the ball-receiving space defined by the first inclined ramp portion of the valve member cup and the opposing second inclined ramp portion of the base means. Such a feature is particularly advantageous in a roll-over valve having an atmospheric vapor release valve due to a significant reduction in interior space within the valve housing available for ball movement necessitated by inclusion of such an atmospheric vapor release valve as will be explained hereinafter.
Additional features and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of the preferred embodiment exemplifying the best mode of carrying out the invention as presently perceived.